This invention relates to the art of ice making machines, and more particularly to an improved ice making machine employing a compression refrigeration system for the production of ice, by freezing a given quantity of water in an ice forming enclosure, and harvesting and collecting the formed ice, with the machine cycled through its freezing and harvesting operations to provide a continuous supply of a given quantity of ice.
A variety of machines have previously been evolved for automatically producing ice cubes. Such previously evolved ice making machines have employed a compression refrigeration system having a refrigerant compressor and condenser coupled in a refrigerant flow circuit with an evaporator coil arranged in heat exchange relationship with an ice forming enclosure such as a grid of ice forming cells having a movable closure platen at the bottom of the cells, as shown by U.S. Pat. Nos. 3,009,336; 3,277,661; 3,850,005; and 3,964,270. As disclosed in U.S. Pat. No. 3,009,336, it is recognized that a plurality of separate ice making machines, each with its own compression refrigeration system may be conjoined by stacking one above the other, with the ice produced by one grid dropping through a lower machine into a common bin. Each of these ice making machines, though feeding their output to a common ice collecting bin employs separate compressor systems, and separate control systems, increasing the cost of the apparatus, and the volume requirements for the installation of the apparatus.
The expense of providing separate compressors, compressor motors and a condenser and condenser fan for each set of ice forming cells results in obvious inefficiencies. Further, the heat generated by the compressor/condenser units enclosed within a housing common to the ice forming cells decreases the efficiency of operation of these units.
Additionally, problems of accuracy and maintenance were found in control systems employed to regulate the operation of the prior art ice making machines so as to produce the desired sequence of freezing and harvesting cycles. Thus, in the machine disclosed in U.S. Pat. No. 3,009,336, desired control is achieved by employing a weight control utilizing a so-called "pilot tank" and "control stream nozzle." The nozzle diverts the supply water from the pilot tank when the cells of the ice forming grid are filled, reducing the water in the pilot tank causing it to lighten and permit actuation of a circuit initiating ice harvest. As is apparent, the accuracy of this pilot tank often leaves much to be desired, and production costs and maintenance and adjustment requirements are generally excessive.
In U.S. Pat. No. 3,277,611, an attempt was made to eliminate the problems with the pilot tank by utilizing a thermostatic temperature response arrangement, with the thermostat sensing temperatures in the ice forming chamber, presumably indicative of the presence of ice. A plurality of thermostats were employed, one thermostat responsive to a first relatively high temperature indicative of the fact that there is no ice in the freezing chamber to initiate the freezing cycle; and a second thermostat responsive to a given low temperature indicative of the fact that any water in the freezing chamber would be frozen. Though the use of thermostat controls eliminates the problems with the pilot tank, it is found that with aging, and irregularities in the ambient atmosphere in which the ice making equipment is located, relatively extensive servicing of the equipment is required to adjust and maintain the setting of the thermostats to maintain the desired freezing.
In U.S. Pat. No. 3,964,270, it was attempted to eliminate the problems of thermostat maintenance by combining a timer with a single thermostat, on the assumption that when a given temperature has been attained for a given period of time, either desired harvesting or ice formation had been obtained. However, it is found that with time, even utilizing a single thermostat, temperature measurements are inaccurate, and maintenance problems increase.
Even with all of the aforedescribed systems, where it is desired to employ a single compressor/condenser assembly to handle a plurality of separate evaporators, no control system responsive only to the conditions in any one of the refrigerant compartments would suffice to provide desired operation.